Donald Trump, a 21st century leader who does business all over the world, owns his jet and governs with tweets, has staked his presidency on a wall, the most medieval of civic symbols.
In the last decades, when half a dozen presidents have struggled on how to handle the flow of migrants from the south of the border, conservatives and liberals have often rejected a wall as an old-fashioned tactic, an obtuse tool that could keep some people out, but send a disconcerting message about the American ideals of openness and does not address the factors that drive migrants here in the first place.
Trump, who rarely becomes philosophical, felt compelled to face the morality of a wall in his Oval Office address Tuesday night. The president said that people "do not build walls because they hate people outside, but because they love people inside".
Consciously or not, Trump, who will travel to the border with Mexico on Thursday to press the campaign for a wall, echoed what many historians have said about why even the most modern societies continue to build walls: "Building a wall or a fence, you're defining your community, "said Gregory Dreicer, a technology historian who studied fences and nationalism.
But the walls have a checkered story to keep the separation between people. No matter how high, how long, how strong the wall is, people have a mysterious talent to find their way above, below and around.
From the biblical Jericho to modern Mexico, walls were set up to stop terrorists, immigrants, armies, drugs, weapons, foreigners, unwanted races and creeds and tribes. The Romans built Hadrian's Wall to keep the barbarians away. The Chinese built the Great Wall to keep out a series of rival nations.
The walls determine the scores and reinforce the rows. The walls have a lasting emotional influence. They are good at sending messages. "Shoot this wall," Ronald Reagan told the Berlin Wall in 1987, and some people believed that a whole empire fell as a result.
Some historians argue that the walls have repeatedly demonstrated their value: they protect communities from perceived threats, bringing people inside the wall into safety and camaraderie.
But walls can also undermine the community, creating and cementing "us against them" antagonisms, allowing bricklayers to avoid solving the problems they face.
"A wall or a gate tells you every day that there are dangerous people right outside who want to destroy you," said Setha Low, an environmental psychologist at the Graduate Center of the City University of New York and author of a book on closed communities. "Rigid barriers create fear."
Like the president, the president of the Chamber, Nancy Pelosi (D-Calif.), It focused not only on the practical question if a wall works, but on the larger message it sends. "A wall, in my opinion, is an immorality," he said. "It is not who we are as a nation".
But the walls and other physical barriers are as American as they can be.
In 1860, the presidential campaign of Abraham Lincoln, trying to brand the candidate as a man of the people, distributed pieces of fencing to the voters, a reminder that Lincoln was a rail separator, a man who, like many American farmers and landowners, he built fences. From the early days of the nation, when only white male landowners could vote, many fences built on their land to show their neighbors that they were eligible, Dreicer said.
In recent decades, US developers have built closed communities to keep criminals, sellers, and vandals out. Today, more than 14% of Americans living in subdivisions live behind walls or gates, according to the Census Bureau's American Housing Survey.
But the walls are also contrary to American ideals of openness and individualism. "Do not intrude me," says a classic song by Cole Porter. "Oh, give me land, a lot of land and the starry sky above / do not lock me in."
Today walls are a popular response to the annoying problem of mass migration in a globalized economy. When in 2015 thousands of Middle Eastern and African refugees poured into Eastern Europe, Hungary started building a 13-foot fence on the border with Serbia. Similarly, Bulgaria has chosen a fence to slow down migrants arriving from Turkey.
But many say the walls are not up to date with a 'sophisticated'. In the Vatican this week, Pope Francis recalled the Berlin Wall as a symbol of the "painful division of Europe" and implored Christians to oppose the "temptation to erect new tents".
The Berlin Wall was built on a lie: Communist East Germany claimed that it was protecting its people from Western invaders; the official name of the structure was the "anti-fascist bulwark". But, in fact, East Germany erected the pen wall in its own citizens, who had been deficient towards the capitalist West in the masses.
Unpopular for each of his 10.316 days, the Berlin Wall remained as long as it did so because it served the purposes of both sides: the East mostly interrupted its brain drain. And many Western leaders were happy to withdraw from a clash with the oppressive Soviet regimes and East Germany.
"A wall is much better than a war," said President John F. Kennedy in 1961.
Governments keep coming back to the walls for two reasons: the walls make some people feel safe. And it is often much easier to build a wall than to solve a problem through law or politics.
"The existence of the wall limits and shapes behavior as much as, if not more, than the law," said Sarah Schindler, associate dean of the University of Maine Faculty of Law, who has studied how obstacles can achieve the political objectives that elected officials can achieve through political means.
For example, while it is unconstitutional to exclude people from a neighborhood based on race or poverty, the US Supreme Court issued a ruling that issued 6 to 3 in 1981 that the city of Memphis could barricade a road linking a neighborhood white to black. White residents had demanded that the road be closed to alleviate "traffic pollution" and prevent "unwanted traffic".
The court rejected black residents' claims that the barrier was meant to divide races. "The fact that most drivers who will be bothered by the action are black" was simply of "symbolic meaning," the court said.
Trump's promise to build a wall along the almost 2000 miles of the US-Mexico border is certainly not new. In 1996, Clinton's "Operation Gatekeeper" initiative installed fences, walls, sensors and lights to stop the flow of illegal immigrants. The net effect was to move the migration from the San Diego area to the Arizona desert.
In 2007, George W. Bush's administration launched a $ 7.6 billion program to add walls, fences, cameras and other technologies to create an "effective control" of the border. This also did not work much.
"A wall is so primitive," said Jane Loeffler, an architectural historian who studied the fortification of US embassies after the bombing of 1983 at the US Embassy in Lebanon. "You can dig under it, climb over it, catapult us over." A wall is more symbolic than a true defense, a wall is fear in three dimensions. "
The example that Trump often quotes from a successful wall is the 267-mile barrier – part wall, part fence – that Israel built in the West Bank to keep out the Palestinian suicide bombers. The number of bombs actually decreased: 450 Israelis were killed by suicide bombers in 2002. Just 13 died in 2007 after the barrier was completed.
The Palestinians say the huge decline stemmed mainly from the security efforts of the Palestinian Authority. Meanwhile, the wider impact of the barrier has been mixed.
"The Israelis say they feel much safer," said Low, "but the wall also deepened the social divide, making it even more difficult to cross."
Walls have a huge advantage over laws, norms and other immaterial efforts to govern behavior. The rules only work thanks to people's goodwill, the recognition of a social pact on who we want to be, and the expectation that those who break the rules will be shamed or punished.
Walls do not require this consensus – and may reserve a special appeal for a president who came to the office as a builder, a developer who repeatedly acted on his belief that the facts in the field would usually beat the code books.
The proponents of the walls take courage in their clarity. In 2010, when former Alaska Governor Sarah Palin learned that a journalist who was planning to write a book about her was moving into the next house, Palin said she would simply build a fence, which she he claimed to be anything but an act of aggression.
Quoting Robert Frost's classic poem, "Mending Wall," best known for the phrase "Good fences make good neighbors," Palin brought Frost to mean that a fence can improve relationships with people living nearby.
But the poet was ironic; his point was that the walls separate us from one another. "There's something he does not like a wall / He wants it down," wrote Frost. He saw his wall neighbor as an unrepentant slogan, amassing rocks on top of another "like an old savage armed with stone".
A century ago, Franz Kafka declared the Great Wall of China a failure of human imagination, writing in a story that a wall can not protect.
"The structure itself is in constant danger," he wrote. "Human nature, which is fundamentally uncaring and by nature like the swirling dust, is not restricted, and will soon begin to shake off restrictions and to snatch walls".
However, walls continue to be built because they are part of what we are. "Walls can be important symbols and can have some effect," said Dreicer. "The Berlin Wall prevented the East Germans from leaving for a long time, but as with most walls, one could see from the beginning that it was only condemned."